1. Field of Invention
The invention relates to a control device for a hybrid vehicle driving device that includes an internal combustion engine and an electric motor as drive force sources and that is capable of realizing a motor-powered travel of the hybrid vehicle in which only the electric motor is used as a drive force source during a state where the rotational driving of the internal combustion engine is stopped, and also relates to a control method for the driving device. More concretely, the invention relates to a technology of controlling the supply of lubrication oil to a power transmission device performed by a lubrication oil supply device that supplies lubrication oil due to the rotational driving of the internal combustion engine.
2. Description of Related Art
A well-known control device for a hybrid vehicle driving device includes an internal combustion engine and an electric motor as drive force sources, a power transmission device that transmits power of the drive force sources to driving wheels, an electric storage device that supplies electric power stored therein to the electric motor, and a lubrication oil supply device that is operatively linked to the internal combustion engine and supplies lubrication oil to at least a portion of the power transmission device due to the rotational driving of the internal combustion engine.
An example of this technology is a control device for a hybrid vehicle driving device described in Japanese Patent Application Publication No. 2003-63258 (JP-A-2003-63258). This control device for a hybrid vehicle driving device includes, as a power transmission device, a planetary gear device that has a first element linked to the engine, a second element linked to the first electric motor, and a third element linked to the transmission member and a second electric motor, and that distributes the output of the engine to the first electric motor and the transmission member. The control device is capable of realizing a motor-powered travel of the hybrid vehicle in which only the second electric motor is used as a drive force source during a state where the rotational driving of the engine is stopped.
Besides, this control device for a hybrid vehicle driving device includes an oil pump linked to the output shaft of the engine. Using the oil pump that is rotationally driven when the engine is operated, the control device supplies lubrication oil to various portions (e.g., gears, bearings, etc.) of the planetary gear device and other power transmission devices. However, since the oil pump linked to the output shaft of the engine is not rotationally driven during the motor-powered travel during which the rotational driving of the engine is stopped, there is a possibility that during the motor-powered travel, necessary supply of lubrication oil to various portions of the power transmission devices may fail and therefore rotating members, such as gears and the like, may undergo seizure or the like and therefore decline in durability. For example, if it may be possible to supply lubrication oil to various portions of the power transmission devices by the well-known differential ring gear or the like splashing up lubrication oil accumulated in the power transmission devices, lubrication can be accomplished, for example, on the meshing portions of tooth surfaces of gears and the like, but there is a possibility of failure of sufficient supply of lubrication oil to interiors of the planetary gear device, bearings, etc.
Therefore, Japanese Patent Application Publication No. 2003-63258 (JP-A-2003-63258) proposes that in the case where a predetermined condition is satisfied while the operation of the engine is stopped, concretely, in the case where a predetermined time (e.g., a constant time or a time determined according to the lubrication oil temperature) has elapsed after the engine stops, the engine be rotationally driven by driving the first electric motor for a predetermined time to rotationally drive the oil pump so that lubrication oil is supplied to various portions in the power transmission devices.
However, even while the predetermined time has not elapsed after the engine stops, the supply of lubrication oil to various portions in the power transmission devices becomes needed in the case where the travel distance in the motor-powered travel is long, or in the case where the travel distance is predicted to be long. On the other hand, even after the predetermined time has elapsed after the engine stops, the supply of lubrication oil to various portions in the power transmission devices is not needed in the case where the travel distance in the motor-powered travel is short, or in the case where the travel distance is predicted to be short.
Hence, if the engine is rotationally driven in a fixed fashion when a predetermined time elapses after the engine stops as in Japanese Patent Application Publication No. 2003-63258 (JP-A-2003-63258), there is a possibility of decline in the energy efficiency, for example, the fuel consumption efficiency.
Particularly in a so-called plug-in hybrid vehicle capable of charging the electric storage device from a household electric outlet or the like, the above-stated problem may become conspicuous due to its increased frequency of the motor-powered travel.